Ion-implanted magnetic bubble memories are disclosed in U.S. Pat. No. 3,792,452 of M. Dixon, R. A. Moline, J. C. North, L. W. Varnerin, Jr., and R. Wolfe issued Feb. 12, 1974. The patent shows a familiar magnetic bubble memory organization commonly referred to as a major-minor organization. A bubble memory organized in such a manner is characterized by a plurality of closed loop paths termed "minor" loops and at least one major path. A bubble generator and a detector are associated with the major path, and data, represented by a bubble pattern, are moved between ends of the minor loops and the major path typically at transfer ports.
If first and second major paths are used, they are associated with opposite ends of the minor loops with the generator associated with one path and the detector with the other. The transfer function is implemented in this latter case so that transfer-into the loops and transfer-out of the loops occurs as separate functions in the first and second paths respectively. If the first and second paths are connected to form a single major path or loop, a data inversion occurs which, for permalloy bubble memories, is corrected by the familiar G-shaped major-minor organization.
When ion-implantation is employed to define bubble propagation paths, those paths typically are defined at the edge of nonimplanted regions (actually the bubbles reside in the adjacent implanted region) which have interlaced bulges and cusps formed, for example, by contiguous discs. Movement from one path, so formed, to another requires movement across an implanted region. Particularly, for G-shaped major loops a problem arises in that topological constraints preclude separate transfer-out and transfer-in ports from being defined in any obvious ways simply because the bubbles cannot be aligned for transfer into the same loops that they were transferred out from. In a general way this is due to the absence of sufficient numbers of implanted areas for traversal by bubbles where transfer ports are required.